VSTO "Orcas" Ribbon Designer
Kathleen McGrath has a great blog post about her favorite feature in the upcoming "Orcas" release of VSTO, the new Ribbon Designer. The Ribbon Designer lets you extend the Office 2007 Ribbon interface with your own controls. She even includes a video walkthrough of using the designer to create tabs, groups, and buttons. She also points out some limitations in the Ribbon designer in that you can't directly reuse the button events from the Office product, i.e. you can't add a new button that calls Word's built-in Bold functionality. Hopefully this is something that will be addressed in later CTPs.